Histidine was first isolated by German physician Albrecht Kossel and Sven Gustaf Hedin in 1896. It is also a precursor to histamine, a vital inflammatory agent in immune responses.
The acid-base properties of the imidazole side chain are relevant to the catalytic mechanism of many enzymes. In a histidine proton shuttle, histidine is used to quickly shuttle protons. It can do this by abstracting a proton with its basic nitrogen to make a positively charged intermediate and then use another molecule, a buffer, to extract the proton from its acidic nitrogen.
Histidine forms complexes with many metal ions, for example the axial base attached to Fe in myoglobin and hemoglobin.
* Amino acids which are essential amino acids which cannot be made by the human body and, therefore, must be obtained in the diet.
Tillery, Enger and Ross